Arthur Holmes's "Principles of Physical geology" is recognized as a seminal work which has influenced generations of geology students from many countries in its first three editions. But in the light of continuing new discoveries from sophisticated geophysical exploration methods, deep drilling in the oceans and on land, and satellite imagery, much of the theoretical aspects now requires substantial revision. This fourth edition returns to the three-part structure of the original book. After a preliminary survey of the subject, the second part describes the external processes affecting the Earth's crust and the final part, dealing with plate tectonics and continental drift, is entirely new. Each chapter has been reviewed or rewritten. Two-colour diagrams aid the understanding of stratigraphy and map work, and a full colour plate section shows some spectacular examples of geological features from around the world.